feat: brain.auditGraph() — read-only graph-truth audit

- New public API: walks every canonical relationship record, queries the same
  read path applications use (related() with all visibility tiers included),
  and classifies every discrepancy into its failure family: missingFromReads
  (records the read path omits — stale adjacency), danglingEndpoints
  (endpoint entity gone — the partial-delete scar class), readOnlyVerbIds
  (read-path edges with no canonical record — ghosts). Design-hidden
  internal/system edges are counted separately so intentional hiding is never
  misclassified as loss. Counts exact; example lists capped with an explicit
  truncatedExamples flag; loud narration on incoherence; mutates nothing.
- Classification core lives in src/graph/graphAudit.ts behind injected seams
  (canonical walks + the end-to-end read) so the discrepancy logic is testable
  in isolation; brainy wires the seams to storage walks and related().
- getNounIdsWithPagination now refuses an undecodable resume cursor loudly —
  the third and final pagination walk brought under the 8.5.2 cursor contract.
- Types exported: GraphAuditReport, GraphAuditDiscrepancy. Docs: the
  inspection guide gains the audit -> repair -> audit verification ritual.

src/storage/baseStorage.ts

@@ -2230,6 +2230,14 @@ export abstract class BaseStorage extends BaseStorageAdapter {
 
     const { limit, offset = 0, filter } = options
     const cursor = this.decodeNounWalkCursor(options.cursor)
+    if (options.cursor && cursor === null) {
+      // Same law as getNouns/getVerbs: an undecodable resume token FAILS
+      // instead of silently restarting the walk at offset 0.
+      throw BrainyError.storage(
+        `getNounIds: invalid pagination cursor '${options.cursor}' — cannot resume this walk. ` +
+          `Restart it without a cursor.`
+      )
+    }
     const collected: Array<{ id: string; shard: number }> = []
     const peekCount = cursor ? limit + 1 : offset + limit + 1
     const startShard = cursor ? cursor.shard : 0